Various photonic devices rely on optical interference (between multiple light paths) for modulating the amplitude, routing or switching of optical signals. Generally, this is achieved by splitting the optical signal equally between two waveguides and modifying the optical phase of one waveguide relative to the other. Devices based on this interferometric principle include optical switches for telecommunication wavelength bands such as the 1310 nm or 1550 nm bands. Optical phase modification is achieved by changing the refractive index in one or both of the paths.
The thermo-optic effect can be applied to change the refractive index in one of the paths by a local heating element, while the other path remains nominally at ambient temperature. The temperature difference created in this manner can produce the required optical phase difference between the two paths. However, maintaining the temperature difference in the optical switching element requires the consumption of electrical power, the level of which is determined by the electric current applied to achieve a desired state of the photonic switching element. As the desired state is changed to a different setting, the required temperature difference in the two waveguides needs to be adjusted by altering the thermal power and the electric current required to produce it. As the number of optical switch elements and complexity increases, more electrical power is required to drive the optical switch, leading to rise in thermal power dissipation and introducing cooling problems. Further, as the configuration of the optical switch changes during operation, temperature gradients across the switch elements can lead to thermal crosstalk between the elements, which could adversely affect switch operation and possibly require additional complexity in monitoring and controlling the switch elements. There is a need for an improved thermal optical switch control.